Method of application of micro-priming spots



1959 R. H. WEINGRAD ETAL 2,873,642

METHOD OF APPLICATION OF MICRO-PRIMING SPOTS Filed April 18, 1957 IN V EN TORS,

Rlchord H. Weingmd BY Petey B. Ferraro wllllflm R SmHh,Jn

United States PatctitD" METHOD OF APPLICATION OF MICRO-PRIMIN SPOTS Richard H. Weingrad, Rockville, and Peter B.- Ferrara and William P. Smith, Jr., Silver Spring, Md., assignors to the United States of America as represented by the Secretary of the Army Application April.18, 1957, Serial No. 653,718

' 1 Claim." 01. 861-1) (Granted under Title 35, U. S. Code (1952), see. 266) The invention described herein may be manufactured and used by-or for the Government for governmental purposes without the payment to us of any royalty thereon.

This invention relates to explosive devices and more particularly to a method for application of micro-priming spots to initiator or delay element plug assemblies;

In the manufacture of certain explosive initiators or delay elements, it is often required that a small accurate quantity of priming mixture be applied. The present method of application involves tedious relatively inaccurate manual application employing means such as a wire loop or brush. As a necessary consequence, this method results in a fairly high incidence of delay element malfunctioning or rejects due to either excessive or insutficient amounts of the priming mix applied to the delay element plug assemblies.

An object of this invention is to provide a continuous automatic transfer process for the application of micro priming spots.

Another object is to provide a method for application of an accurately measured amount of priming mixture or explosive to an initiator or delay element plug assembly.

Still another object is a method for application of accurate charges of explosive primer material for delay elements, which method is capable of producing very accurate short time delay intervals.

A further object is an extremely safe and efiicient method for handling and applying micro-priming spots.

A still further object is a method of priming spot application capable of producing an initiator bridge assembly possessing improved strength, stability and rigidity.

An important object is to provide a method of priming spot application capable of producing an initiator in which variables in detonating function are virtually eliminated.

Briefly the method of this invention involves the punching of a disc from a primer-coated carrier onto an adhesive surface of an initiator assembly. Upon proper curing of the composite structure a relatively accurate preset delay element is obtained.

The specific nature of the invention, as well as other objects, uses, and advantages thereof, will clearly appear from the following description and from the ac companying drawing, in which:

The figure is a sectional view of apparatus for applying priming spots in accordance with the present invention.

The method presented by the present invention may best be understood with reference to the drawing.

A primer mixture 10 such as lead styphnate containing or suspended in a binder lacquer or similar material possessing adhesive and heat consumable properties and characteristics may be supported on carrier 12. Carrier 12 may assume any suitable configuration and is preferice ably provided in strip form, the length of which may be selectively varied to be commercially available on rolls. In addition, carrier 12 may be relatively thin and for some practical applications can assume a thickness of 0.003 inch. Paper or other suitable material performs .satisfactorily as carrier 12.- Mixture 10 mayalso selectively vary in thickness according to specified requirements and for some intended uses is 0.010 to 0.015 inch thick. Mixture 10 can be applied to carrier 12 by many coatings or other suitable techniques. This composite strip may then be allowed to dry in an oven at approximately 60 to 70 degrees C. to etfect proper-curing.

At predetermined intervals along carrier 12, mixture 10 may be interrupted by a non-consumable barrier or non-application of mixture 10 either transversely, longitudinally or both. This may be an added safety feature to prevent sympathetic detonation of the entire strip should one end be accidentally ignited.

The primer may also be conveniently applied to carrier 12 by initially coating in any suitable manner a consumable binding agent or adhesive on carrier 12 and then supporting the primer thereon by coating or the like, followed by a suitable curing operation.

The initiator or plug assemblies .14 are manually, mechanically or automatically placed or supported in a suitable holder 16 or series of holders. Assembly 14 may feature a bridge or similarly purposed electrical filament 18 which in turn may be suitably supported or partially housed in base 20 in any well known manner.

A light application of a lacquer binder solution or suitable adhesive which may be of a consumable nature is preferably applied to the plug assemblies 14 and still more preferably on and in close proximity to bridge 18 on that area designated generally at 22.

Carrier 12 with the cured coating 10 thereon is preferably supported on a suitable die plate 24 which is conveniently suspended or mounted over holder 16. Plate 24 is provided with an aperture 26 through which a punch 28 may reciprocate manually, mechanically or automatically. A plurality of punch-aperture combinations may be employed to conform with the amount of plug assemblies or desired method of mass production contemplated as will be readily understood by those skilled in the art in view of the present teachings. Coating 10 is preferably in juxtaposition with plate 24 substantially as shown and aperture 26 with its companion punch 28 are preferably disposed directly over that porprimer mix- 22. As shown in the figure, disc 30 is carried by the end of punch 28 during its downward movement. The carrier 12 of disc 30 functions as a reinforcing means and may be permitted to remain on the primer spot 30 to be ultimately consumed when the explosive action takes place.

The next step in preparing the assembly may be to spray lightly over the entire surface of the plug with a thin solution of a lacquer or other suitable consumable coating.

The composite units may then be oven dried at temperatures approximating 60 to 70 C. to effect proper curing of the various coatings applied.

Assembly 14 may utilize two exposed terminals in stead of bridge 18. Accordingly, a conductive or semiconductive material which preferably is relatively inert may be suitably coated on or incorporated in primer mixture 10 to be ultimately in contact with the exposed terminals. An aqueous suspension of the inert material Patented "Feb. 17, 1959 may be employed for suitable coating applications and may be applied immediately after application of mix ture 10 to take advantage of the adhesiveness of the latter while in an uncured state.

The method of application of the primer spot described terminals in close proximity to one another and incorporat-ing' aconductive-bridge therebetween; applying a binder lacquer to said bridge; punching a disc from a carrier having a cured coating of a primer lacquer thereon; continuing the punching movement so that said disc is carried to said bridge and pressed thereagainst with said coating of conductive material in contact with said binder lacquer; spraying the assembled structure with a consumable lacquer; and oven-drying said assembled 10 structure to provide a rigid resultant structure.

References Cited in the file of this patent UNITED STATES PATENTS 720,073

Schmitt et' a1. Feb. 10, 1903 Burrows et al. June 18, 1940 Lawrence Jan. 15; 1957 

